As one of methods of improving the frictional wear property of a resinous article, so-called “gan-pla,” which is made by adding lubricating oil to resinous material, is known. In this method, the resin and the lubricating oil are melted, kneaded, pelletized to obtain a mixture thereof having a certain configuration, and injection-molded or extrusion-molded. The amount of the lubricating oil which can be added to the resin is up to about 10 vol % to prevent deterioration of the injection moldability. Because the resin and the lubricating oil are melted and kneaded, the resinous material has a high uniformity and oil-retaining performance, and the lubricating oil little bleeds out to the surface thereof. Therefore the function of the resinous article in feeding the lubricating oil is insufficient. Further when the resinous article is used as a sliding bearing, a sufficient lubricating performance is not obtained in a region in which a PV value which is the product of a load (P) and a sliding speed (V) is high.
Heretofore as an oil-containing resin, developed to solve the above-described problem, which is a mixture of resin and lubricating oil to be molded into a predetermined configuration, the composition containing the ultra-high-molecular-weight polyethylene and grease is disclosed (see patent document 1). Because the grease of the composition prevents the lubricating oil from flowing, the lubricating oil can be contained in the resin at not less than 50 vol %. The amount of bleeding of the lubricating oil to the surface of the composition is larger than the amount of bleeding of the lubricating oil to the surface of the resinous article formed by the gan-pla.
There is disclosed the oil-containing resin to which the fibrous oil guide article is added (see patent documents 2 through 4); the lubricating oil retained by the porous silica is mixed with the synthetic resin to obtain the oil-containing resin (see patent document 5). These oil-containing resins are intended to successively feed the surface of the resin with the lubricating oil. Owing to the help of the guide material and the porous silica, the amount of the lubricating oil that can be contained in the resin is increased to about 20 vol %.
In the patent document 1, however, although a sufficient amount of the oil is secured, the composition has a high oil-retaining performance, and a utilization efficiency of the added lubricating oil is low because the composition is of an incorporating type of preliminarily mixing the resin and the lubricating oil with each other. And another problem is that the mechanical strength of the oil-containing resinous article is low because it contains a large amount of lubricating oil.
In the oil-containing resins disclosed in the patent documents 2, 3, 4, and 5, as described above, owing to the oil guide materials and the porous silica, the amount of the lubricating oil in the resin is increased to about 20 vol %. Further owing to the addition of the reinforcing agent, a decrease of the mechanical strength of the oil-containing resins can be restrained. But when the oil-containing resins are applied to a retainer of a bearing to lubricate it with only the oil in the resin, there occur problems that the amount of the lubricating oil is insufficient and that the bleeding speed thereof to the surface is low.
Further the methods disclosed in the patent documents 1 through 5 are intended to shape the preliminarily kneaded resin and lubricating oil into predetermined configurations and, therefore, the methods have a limitation in the combination of the resin and the lubricating oil and are unapplicable to a wide range of use.    Patent document 1: Japanese Patent Application Laid-Open No. 6-41569    Patent document 2: Japanese Patent Application Laid-Open No. 11-166541    Patent document 3: Japanese Patent Application Laid-Open No. 2000-71243    Patent document 4: Japanese Patent Application Laid-Open No. 2000-71244    Patent document 5: Japanese Patent Application Laid-Open No. 2002-129183